Charge transport in organic semiconductors is notoriously extremely sensitive to the presence of disorder, both internal and external (i.e., related to interactions with the dielectric layer), ...especially for n‐type materials. Internal dynamic disorder stems from large thermal fluctuations both in intermolecular transfer integrals and (molecular) site energies in weakly interacting van der Waals solids and sources transient localization of the charge carriers. The molecular vibrations that drive transient localization typically operate at low‐frequency (<a‐few‐hundred cm−1), which makes it difficult to assess them experimentally. Hitherto, this has prevented the identification of clear molecular design rules to control and reduce dynamic disorder. In addition, the disorder can also be external, being controlled by the gate insulator dielectric properties. Here a comprehensive study of charge transport in two closely related n‐type molecular organic semiconductors using a combination of temperature‐dependent inelastic neutron scattering and photoelectron spectroscopy corroborated by electrical measurements, theory, and simulations is reported. Unambiguous evidence that ad hoc molecular design enables the electron charge carriers to be freed from both internal and external disorder to ultimately reach band‐like electron transport is provided.
Molecular vibrations govern the charge transport in organic semiconductors, which is limited by different sources of disorder. Understanding and mastering the disorder in these materials can drive the design of better semiconductors featuring band‐like transport.
In this study, a comprehensive investigation of the role of sulfur vacancies on the electronic structure and surface reactivity of molybdenum disulfide is presented. A 2H-MoS2 single crystal was ...annealed at two different temperatures, namely, 300 and 500 °C in vacuum, in order to generate sulfur vacancies in a controlled manner. The detailed characterization of the electronic structure by means of X-ray and ultraviolet photoelectron spectroscopy clearly evidences the formation of a strong surface dipole as well as surface band bending due to the excess of negative charge on the Mo centers, as a consequence of the generated sulfur vacancies. After thermal treatment, a mercaptoundecylphosphonic acid molecule, which consists of a thiol (S–H) tail group and a phosphonic acid group on the other end, was covalently attached on the surface through wet chemical functionalization in order to refill the sulfur vacancies. As a consequence of the vacancy refilling, the surface band bending is reversed and the surface dipole is remarkably decreased, being close to the initial value of the pristine surface.
Hybrid inorganic/organic semiconductor heterojunctions are candidates to expand the scope of purely organic or inorganic junctions in electronic and optoelectronic devices. Comprehensive ...understanding of bulk and interface doping on the junction's electronic properties is therefore desirable. In this work, we elucidate the energy level alignment and its mechanisms at a prototypical hybrid pn-junction comprising ZnO (n-type) and p-doped N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (α-NPD) as semiconductors, using photoelectron spectroscopy. The level alignment can be quantitatively described by the interplay of contact-induced band and energy level bending in the inorganic and organic component away from the interface, and an interface dipole due to the push-back effect. By adjusting the dopant concentration in α-NPD, the position of the frontier energy levels of ZnO can be varied by over 0.5 eV and that of α-NPD by over 1 eV. The tunability of this pn-junction's energy levels evidences the substantial potential of the hybrid approach for enhancing device functionality.
Complications following facial cosmetic injections have recently heightened awareness of the possibility of iatrogenic blindness. The authors conducted a systematic review of the available literature ...to provide the best evidence for the prevention and treatment of this serious eye injury.
The authors included in the study only the cases in which blindness was a direct consequence of a cosmetic injection procedure of the face.
Twenty-nine articles describing 32 patients were identified. In 15 patients, blindness occurred after injections of adipose tissue; in the other 17, it followed injections of various materials, including corticosteroids, paraffin, silicone oil, bovine collagen, polymethylmethacrylate, hyaluronic acid, and calcium hydroxyapatite.
Some precautions may minimize the risk of embolization of filler into the ophthalmic artery following facial cosmetic injections. Intravascular placement of the needle or cannula should be demonstrated by aspiration before injection and should be further prevented by application of local vasoconstrictor. Needles, syringes, and cannulas of small size should be preferred to larger ones and be replaced with blunt flexible needles and microcannulas when possible. Low-pressure injections with the release of the least amount of substance possible should be considered safer than bolus injections. The total volume of filler injected during the entire treatment session should be limited, and injections into pretraumatized tissues should be avoided. Actually, no safe, feasible, and reliable treatment exists for iatrogenic retinal embolism. Nonetheless, therapy should theoretically be directed to lowering intraocular pressure to dislodge the embolus into more peripheral vessels of the retinal circulation, increasing retinal perfusion and oxygen delivery to hypoxic tissues.
Risk, V.
Molecular switches enable the fabrication of multifunctional devices in which an electrical output can be modulated by external stimuli. The working mechanism of these devices is often hard to prove, ...since the molecular switching events are only indirectly confirmed through electrical characterization, without real-space visualization. Here, we show how photochromic molecules self-assembled on graphene and MoS
generate atomically precise superlattices in which a light-induced structural reorganization enables precise control over local charge carrier density in high-performance devices. By combining different experimental and theoretical approaches, we achieve exquisite control over events taking place from the molecular level to the device scale. Unique device functionalities are demonstrated, including the use of spatially confined light irradiation to define reversible lateral heterojunctions between areas possessing different doping levels. Molecular assembly and light-induced doping are analogous for graphene and MoS
, demonstrating the generality of our approach to optically manipulate the electrical output of multi-responsive hybrid devices.
The ITER Neutral Beam Test Facility (NBTF), Padua, Italy, hosts two different experiments: Source for Production of Ion of Deuterium Extracted from Rf plasma (SPIDER), the prototype of the ion source ...(IS) of ITER neutral beam injector (NBI), and Megavolt ITER Injector and Concept Advancement (MITICA), the prototype of the ITER NBI. The ISs of SPIDER and MITICA are driven by radio frequency (RF) power, for a total of 800 kW at 1 MHz. The RF power is delivered to the inductively coupled plasma drivers of the IS by four tetrode oscillators. Operation of SPIDER at high power pointed out the presence of RF stray currents circulating in the electric system. These currents hinder the correct operation of the system, causing damage to its components. To improve the comprehension of the issue, after an overall circuital investigation and the identification of a possible reclosing path for the RF stray currents, a simplified model of SPIDER electric system was developed, initially focusing on a single RF circuit. The aim of the work presented in this article is to extend the model to four RF circuits, to study the impact of their mutual coupling and of the common potential references on RF stray currents magnitude, with a view to improve the comprehension of the issue and the effect of the provisions to mitigate it. The results obtained with this model are compared to SPIDER experimental measurements for validation.
The European DEMO will make use of a significant additional heating power, which could be partly provided by neutral beam injectors (NBIs), which accelerate negative ions by means of grids placed at ...increasing potentials. These grids will be fed by the acceleration grid power supply (AGPS), divided in a number of stages, which has to provide an overall dc voltage down to <inline-formula> <tex-math notation="LaTeX">-</tex-math> </inline-formula>1 MV and currents in the order of tens of Amperes. The AGPS will have to satisfy a set of static and dynamic requirements, mainly in terms of ripple, accuracy, and rise time. In addition, during the NBI operation, frequent losses of insulation between the grids, called breakdowns (BDs), are expected. The AGPS will be able to handle such events by nullifying the output currents as fast as possible in order to limit the energy discharged onto the grids. Adopting the modular multilevel converter (MMC) technology for the AGPS of DEMO and future tokamaks seems promising, due to its intrinsic properties of modularity, high efficiency, fast dynamic response and small energy transferred to the arc in case of BD. Since the converter will be air-insulated, one of the main drawbacks is the large volume occupied. This can be partly reduced by adopting alternative MMC schemes, to minimize the number of components and optimize the counter-voltage applied by the converter at BD. In this article, alternative topologies for the MMC submodules (SMs) or combinations of different schemes full-bridge (FB), half-bridge (HB) are investigated. After a preliminary design of the converter, the results of numerical simulations carried out with circuit models are shown, with control schemes customized for the NBI operation. The performance of the different solutions in steady-state, dynamic and anomalous conditions are discussed, with particular focus on BD events. Finally, thermal analyses on the converter are carried out, to verify whether natural convection of air can be a suitable cooling method for the power components.
The technological exploitation of the extraordinary properties of graphene relies on the ability to achieve full control over the production of a high‐quality material and its processing by ...up‐scalable approaches in order to fabricate large‐area films with single‐layer or a few atomic‐layer thickness, which might be integrated in working devices. A simple method is reported for producing homogenous dispersions of unfunctionalized and non‐oxidized graphene nanosheets in N‐methyl‐2‐pyrrolidone (NMP) by using simple molecular modules, which act as dispersion‐stabilizing compounds during the liquid‐phase exfoliation (LPE) process, leading to an increase in the concentration of graphene in dispersions. The LPE‐processed graphene dispersion was shown to be a conductive ink. This approach opens up new avenues for the technological applications of this graphene ink as low‐cost electrodes and conducting nanocomposite for electronics.
Graphene dispersions: A simple method is reported for producing homogenous dispersions of unfunctionalized and non‐oxidized graphene nanosheets in 1‐methyl‐2‐pyrrolidinone (see picture). Simple molecular modules are used, which act as dispersion‐stabilizing compounds during a liquid‐phase exfoliation process, leading to an increase in the concentration of graphene dispersions.
Here we present the formation of predominantly sp2-coordinate carbon with magnetic- and heteroatom-induced structural defects in a graphene lattice by a stoichiometric dehalogenation of ...perchlorinated (hetero)aromatic precursors hexachlorobenzene, C6Cl6 (HCB), and pentachloropyridine, NC5Cl5 (PCP) with transition metals such as copper in a combustion synthesis. This route allows the build-up of a carbon lattice by a chemistry free of hydrogen and oxygen compared to other pyrolytic approaches and yields either nitrogen-doped or -undoped graphene domains depending on the precursor. The resulting carbon was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, photoelectron spectroscopy (XPS), and SQUID magnetometry to gain information on its morphological, chemical, and electronic structure and on the location of the nitrogen atoms within the carbon lattice. A significant lowering of the magnetization was observed for the nitrogen-doped carbon obtained by this method, which exhibits less ordered graphene domains in the range of approximately 10–30 nm as per TEM analysis compared to the nondoped carbon resulting from the reaction of HCB with larger graphene domains as per TEM and the presence of a 2D mode in the Raman spectra. The decrease of the magnetization by nitrogen doping within the sp2-coordinate carbon lattice can be attributed to an increase in pyrrole-type defects along with a reduction in radical defects originating from five-membered carbon ring structures as well as changes in the π-electron density of edge states.
The Divertor Tokamak Test (DTT) facility is a controlled thermonuclear fusion device, whose construction has started at the ENEA Research Center in Frascati, Italy, with the aim to study solutions to ...mitigate the issue of power exhaust in an integrated environment and operating conditions relevant for future fusion reactors. A power of 45 MW to the plasma is foreseen and provided by a mix of heating and current drive (HCD) systems comprising electron cyclotron resonance heating (ECRH), ion cyclotron resonance heating (ICRH), and neutral beam injector (NBI). DTT, in the first experimental phase, will exploit the ECRH system, including 16 radio frequency (RF) sources (gyrotrons) with potential collector depressed, each rated for 1 MW power, 170 GHz frequency, and 100 s pulse length. The RF sources are fed in pairs by a high voltage power supply (HVPS) set, composed of one main power supply (MPS) and two body power supplies (BPSs), one for each gyrotron, and by low-voltage (LV) power supplies dedicated to the operation of the auxiliaries of the gyrotrons. This work describes the conceptual design of the HVPS system, the evaluation that led to the definition of its main requirements and to the selection of a reference design. In addition, the novel concept is presented for a dummy load (DL) able to mimic the real gyrotrons operation in normal and abnormal conditions for testing an HVPS set.
PDF
